Ziegler-Natta (Z-N) and metallocene-alumoxane type catalyst systems for the polymerization of olefins are well known in the art. Recently a new, ionic pair type of catalyst has been developed which yields polymers of improved properties compared to those made with conventional type catalysts systems. The first, among various publications, to describe this new system was Turner, et al. in EPA 277,003 and 277,004. EPA 277,003 and EPA 277,004 disclose new cyclopentadienyl based catalyst systems comprising an ionic compound wherein the cyclopentadienyl transition metal component or metallocene is reacted with an activator comprising an anion and a cation; the cation being one which is reactable with a non-cyclopentadienyl ligand of the cyclopentadienyl moiety to yield as the reaction product a neutral ligand derivative, and a cationic metallocene species to which the anion of the activator compound is essentially non-coordinating. EPA 277,003 describes an anion component which comprises a plurality of boron atoms while EPA 277,004 describes an anion species which is a single coordination complex having ligand(s) shielding a central charge-bearing metal or metalloid atom.
These ionic complexes can optionally be placed on a support medium in accordance with that described in PCT WO91/09882 or copending, commonly assigned application U.S. Ser. No. 926,006 filed on Aug. 5, 1992. In accordance with WO 91/09882, the ionic catalyst is physisorbed onto an inert carrier which has been previously dehydrated and treated with an alkyl aluminum solution. The ionic catalyst is not covalently bonded onto the support carrier and is extractable or desorble by solvents.
While improvements in catalyst activity, selectivity, and processing were observed with both the homogeneous and heterogeneous ionic catalyst described above, further improvements are sought for the catalyst system through anion effects as well as to address the issue of catalyst desorption found when hetereogeneous catalyst are used.